We reported previously that murine tumor lysate-pulsed dendritic cells (TP-DC) could elicit tumor-specific CD4+ and CD8+ T cell reactivities in vitro and in vivo. TP-DC treatments could result in regression of well- established s.c. and lung metastases, which could be further enhanced by the systemic administration of low-dose IL-2. Although vaccine studies involving TP-DC have been performed, little, if any, information is available on the effects of phagocytic uptake of tumor lysate on DC biology and function. We have investigated gene expression pattern differences between unpulsed DC and TP-DC, using Affymetrix MG- U74Av2 oligonucleotide arrays, which contain ~12,000 genes and ESTs (expressed sequence tags). Upon 24 hr tumor lysate pulsing, the levels of 87 transcripts increased at least threefold while the levels of 121 transcripts were reduced by one-third or more, with accompanying p-values <0.01. Most of these genes encoded a repertoire of proteins important for DC effector functions including cytokines, chemokines and receptors, as well as antigen presentation, cell adhesion, and T cell activation molecules. Interestingly, we observed a high level of expression of a novel member of the class A scavenger receptor family, MARCO on both mouse and human DC. MARCO is thought to play an important role in the immune response by mediating binding and phagocytosis, but also in the formation of lamellipodia-like structures and of dendritic processes. We propose to to define the biology and potential therapeutic implication of TP-DC expressed MARCO. We hypothesize that modulation of MARCO expression will have substantial effects on TP-DC biology and function in vitro and in vivo. We propose the following Specific Aims: 1. To determine the effect of MARCO expression modulation on TP-DC function in vitro; 2. To determine the effect of MARCO expression modulation on TP-DC trafficking in vivo; 3. To determine the therapeutic efficacy of MARCO expression-modulated TP-DC on antitumor activity in mice. The experimental studies outlined in this renewal application are designed to continue our successful preclinical efforts to generate immunization strategies against cancer based on antigen-presenting DC. The findings could have significant translation to human clinical DC vaccine trials.